Silver halide photographic elements comprise at least one hydrophilic colloid as a binder. In most silver halide photographic elements, gelatin is used as hydrophilic colloid. For example, gelatin is used as the main binder in silver halide emulsion layers, protective layers, filter layers, intermediate layers, antihalation layers, backing layers, subbing layers and so on. Usually, such gelatin layers are treated in photographic uses with aqueous solutions having different pH's and temperatures. Gelatin layers, however, have a poor resistance to water and swell excessively, so that they have a greatly reduced mechanical strength and are easily scratched. In extreme cases, especially at high temperature, the gelatin layers dissolve in aqueous solutions.
A number of classes of compounds are known for increasing water resistance, heat resistance and abrasion resistance of gelatin layers. These compounds are known as hardeners in the photographic art. These include, for example, inorganic compounds such as chromium, aluminum and zirconium salts; aldehydes and halogenated aldehyde compounds such as formaldehyde, glutaraldehyde and muchochloric acid; bisvinylsulfone compounds; bisepoxides; bisacrylamides; halogenated triazines; dioxanes and the like.
In the choice of a hardener, the hardener should meet at least the following conditions.
(1) It should be photochemically inert. In other words, it should not afford chemically adverse effects (e.g., decrease in sensitivity, fading of the latent image, and fogging) on the performance of the silver halide photographic emulsion layer. PA0 (2) It should be chemically stable in solid or solution state. PA0 (3) It should have a sufficient solubility in water so that hardening is liable to be even within the layer. PA0 (4) It should be not harmful to the human body. PA0 (5) It should not react with other photographic additives except the gelatin. PA0 (6) It should have an hardening effect which attains its maximum as soon as possible after drying, so that the degree of hardening will not change for a long period of time due to "post-hardening" and the material which is being hardened will not continuously change its permeability to developer solutions.
A problem has been observed by the Applicant in the hardening of photographic elements in which silver halide emulsions are chemically sensitized with sulfur and gold in the presence of sulfinic acid compounds as antifogging agents. Hardening agents such as halotriazine compounds used in combination with the lo above photographic elements show a high hardening reaction for gelatin and a small post-hardening effect. The main disadvantage with these hardeners is the liberation of hydrogen halides during hardening and consequently fading of the latent image. It is well known that images with the silver halide photographic process are obtained by image exposure for forming latent images and development for converting the latent images into silver images. Latent image fading caused by the halotriazine hardeners has the consequence of lowering the sensitivity of the silver halide photographic element, possibly to unacceptable values. Hardening agents such as vinylsulfone type hardeners used in combination with the above photographic elements have generally a high hardening rate and a small post-hardening effect. The main disadvantage with these hardeners is that they react with sulfinic acid compounds used as antifoggant agents in sulfur and gold sensitized silver halide emulsions. This reaction reduces the hardening power of the vinylsulfone type hardeners and the antifogging property of the sulfinic acid compounds. Additionally, the reaction of the hardener and the sulfinic acid compound produces water-insoluble compounds which can cause defects in the photographic element. The same reaction with sulfinic acid compounds is obtained with other hardeners such as formamidinium type hardeners described in U.S. Pat. No. 4,418,142.
These materials are not capable of satisfactorily hardening a silver halide photographic material in which a silver halide emulsion has been chemically sensitized with sulfur and gold in the presence of a sulfinic acid compound. It is, therefore, an object of the present invention to provide a gelatin-containing silver halide photographic element sulfur and gold sensitized in the presence of a sulfinic acid compound, in which gelatin is efficiently and quickly hardened and no latent image fading occurs.
It has now been discovered that gelatin-containing silver halide photographic elements sulfur and gold sensitized in the presence of sulfinic acid compounds can be hardened without the disadvantages of most previously known hardeners by using a carbamoylpyridinium salt.
Carbamoylpyridinium salt hardeners are known. Details concerning the preparation and properties thereof may be found in U.S. Pat. Nos. 3,880,665, 4,014,862 and 4,063,952. These patents, however, do not suggest the use of said hardeners in gelatin-containing silver halide photographic elements chemically sensitized with sulfur and gold in the presence of sulfinic acid compounds. The fact that the carbamoylpyridinium salt hardeners do not react with sulfinic acid compounds is not reported in the literature and is very surprising.